Welding is a fabrication or sculptural process that joins materials, usually metals or thermoplastics, by causing coalescence. This is often done by melting the workpieces and adding a filler material to form a pool of molten material (the weld pool) that cools to become a strong joint, with pressure sometimes used in conjunction with heat, or by itself, to produce the weld. Many different energy sources can be used for welding, including a gas flame, an electric arc, a laser, an electron beam, friction, and ultrasound. Different types of welding include Gas Tungsten Arc Welding (sometimes referred to as TIG or GTAW welding), Water Cooled welding, Gas Metal Arc Welding (sometimes referred to as MIG or GMAW welding), Shielded Metal Arc Welding (sometimes referred to as STICK or SMAW welding), Oxygen and Acetylene welding (sometimes referred to as Oxy/Acetylene welding), and Plasma Torch welding. Generally speaking, different types of welding require different items of associated equipment of varying shapes, sizes and usage parameters.